Was Canada right to change its breast screening guidelines? Yes

The updated 2018 Canadian Task Force on
Preventive Health Care breast cancer screening guidelines for average
risk women is a welcome change from the more paternalistic guidelines
that we as family doctors receive on a regular basis.

The updated guidelines follow a trend of engaging patients in shared decision making. What we call “patient-centred care.” Patient-centred care encourages patients to feel that they are being treated as a whole person by ensuring that the health care they receive reflects their own values and preferences.

Photo : Toronto Star File

When breast
cancer screening task forces in Canada and around the world review years
of rigorous studies, they continue to see a small benefit of saving
women aged 40 to 74 years from dying of breast cancer. This benefit is
smaller in women under the age of 50 compared to women over 50 years.

To
give you a sense of the difference between age groups, it is estimated
that if you take 1,000 women in each age group and look at death from
breast cancer, screening mammograms will save two lives in women aged 70
to 74, one life in women aged 50 to 69 and less than one life in women
40 to 49 years of age.

Unintended risks are also seen in these
studies. This includes physical and psychological consequences from
false positive results as well as overdiagnosis resulting in unnecessary
treatment of cancer that would not have caused harm in a woman’s
lifetime.

Women less than 50 years of age have a higher
risk of these harms than older women. As an example, it is estimated
that if you take 1,000 women in each age group, screening mammograms
will cause unnecessary biopsies in 30 women aged 70 to 74, in 35 women
aged 60 to 69, in 37 women aged 50 to 59 and 43 in women aged 40 to 49.

Based
on this information, the current 2018 recommendations for average risk
women have not changed much compared to the 2011 guidelines.

For
women aged 40 to 49 years, screening with mammography is not
recommended. For women aged 50 to 74 years, screening with mammography
every two to three years is recommended.

While the recommendations
seem reasonable for large populations of women, they don’t factor in
that individual women may want to make their own decisions on whether or
not they are willing to accept certain risks (including the anxiety
associated with false positive results, potentially unnecessary biopsies
and the potential for overdiagnosis) over a gain of a small potential
benefit of not dying from breast cancer.For the 2018 updated
guidelines, the task force also looked at the results from 29 studies
that explored how women 40 years of age and older rated the importance
of their own personal expected benefits and harms of breast cancer
screening.

This review of patient values and preferences suggested
that many women aged 40 to 49 years would not choose to undergo breast
cancer screening using mammography if they were aware of the risks
commonly seen among women in their age group.

In contrast, many
women aged 50 years and older chose screening given their more
favourable balance of benefits and harms. This led the task force to add
to the 2018 updated recommendations, “the decision to undergo screening
is conditional on the relative value a woman places on possible
benefits and harms from screening.”

For women who are at high
risk, obviously it is a different discussion. Similarly, if women of any
age have any signs or symptoms of breast cancer, such as nipple
discharge, lumps, puckering, dimpling, or skin changes of the breast
they should see their family doctor to discuss a diagnostic mammogram.

As
advances in breast cancer screening, diagnosis and management emerge,
we hope to see significantly less of the risks associated with
mammograms in women who do not have breast cancer as well as less
overdiagnosis and treatment of breast cancers that would have never
caused a problem.

Until then we need to get away from the
one-size-fits-all recommendations and move toward a more personalized
shared decision-making approach to help women decide if a screening
mammogram is right for them. In practice, I still recommend screening
mammograms for most women over age 50 and even for some women under 50.